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posted by martyb on Saturday September 08 2018, @10:24AM   Printer-friendly
from the there-goes-the-neighborhood dept.

Pluto a Planet? New Research from UCF Suggests Yes

The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando. In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to "clear" its orbit, or in other words, be the largest gravitational force in its orbit. [...] [Philip] Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication -- from 1802 -- that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.

[...] The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed. However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger said.

[...] Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape. "And that's not just an arbitrary definition, Metzger said. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body." Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said. "It's more dynamic and alive than Mars," Metzger said. "The only planet that has more complex geology is the Earth."

Planet Ceres, please.

The Reclassification of Asteroids from Planets to Non-Planets (DOI: 10.1016/j.icarus.2018.08.026) (DX)

Related: Pluto May Regain Status as Planet
Earth is a "Dwarf Planet" Because it has not Cleared its Orbit


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  • (Score: 2) by theluggage on Saturday September 08 2018, @07:58PM (4 children)

    by theluggage (1797) on Saturday September 08 2018, @07:58PM (#732289)

    I mean, how do we even define that except for saying that the smaller orbits the larger?

    "Smaller orbits the larger" seems like a perfectly cromulent and easily-defined standard. Obvious alternative would be to say that a "moon" is orbiting a "planet" if the barycentre of the two bodies was inside the planet, otherwise you have a binary planet... However, I think that makes Charon/Pluto a binary so that's another argument to contend with.

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  • (Score: 3, Informative) by requerdanos on Saturday September 08 2018, @08:28PM (3 children)

    by requerdanos (5997) Subscriber Badge on Saturday September 08 2018, @08:28PM (#732300) Journal

    Obvious alternative would be to say that a "moon" is orbiting a "planet" if the barycentre of the two bodies was inside the planet, otherwise you have a binary planet...

    That sounds a lot more tenable than "smaller orbits larger," sure.

    otherwise you have a binary planet... However, I think that makes Charon/Pluto a binary so that's another argument to contend with.

    Heh, no, Charon/Pluto would be "binary biggish rocks" or "binary dwarf planet/smaller thingy combo" or "binary rock soup" but not a binary "planet" since, of course, Pluto is too small to qualify and Charon smaller still.

    The Pluto qualification people are dancing round here seems to be "Historically Identified As Totally A Planet By Ancients Long Dead If It Was Good Enough For Galileo Et. Al. Then Good Enough For All Time" which feels really nice (like "small orbits big") but feels does not make "is" when you are doing science.

    Early astronomers tried hard to figure out how the sun and other planets orbit the Earth here at the center of creation, but despite them being long dead, we don't try to enshrine their beliefs. Pluto's planethood should probably fall into that category as well.

    • (Score: 2) by theluggage on Sunday September 09 2018, @10:05AM (1 child)

      by theluggage (1797) on Sunday September 09 2018, @10:05AM (#732432)

      The Pluto qualification people are dancing round here seems to be "Historically Identified As Totally A Planet By Ancients Long Dead If It Was Good Enough For Galileo Et. Al. Then Good Enough For All Time"

      Only one side is dancing around that definition: I have not seen anyone here arguing that Pluto should be a "planet" but Eris and co. shouldn't. Rather, its the Pluto-demoters who are trying to contrive a pseudo-scientific justification for their (particular) take on tradition. The serious issue is here is not what we call Pluto, but the suggestion that the IAU has voted in wonky science to ensure that the "right people" get bragging rights for discovering planets .

      Its really a simple choice: (a) leave "planet" as a slightly ambiguous historical term (as it was before the IAU put their foot in the pie), or (b) come up with a valid formal definition that has genuine scientific significance (the "sphere" one being the best candidate so far except for the pesky reality of having to accept a few extra planets). I'd probably vote for (a): I'm not a fan of trying to retcon old words with new definitions (see: weight, work, food, vegetable...)

      • (Score: 2) by requerdanos on Sunday September 09 2018, @04:25PM

        by requerdanos (5997) Subscriber Badge on Sunday September 09 2018, @04:25PM (#732492) Journal

        I'd probably vote for (a): I'm not a fan of trying to retcon old words with new definitions

        To me, (b) is the more appealing because I would be excited to see bodies newly recognized as planets, and because I recognize that Eris, Ceres, et. al. wander just as much as Venus and Mars and so I could convince myself that the definition is simply become more precise as science advances.

        I had not thought of the Pluto-demoters in such a political/opinion based way until you pointed this out to me.

    • (Score: 4, Informative) by toddestan on Monday September 10 2018, @02:16AM

      by toddestan (4982) on Monday September 10 2018, @02:16AM (#732628)

      The Pluto qualification people are dancing round here seems to be "Historically Identified As Totally A Planet By Ancients Long Dead If It Was Good Enough For Galileo Et. Al. Then Good Enough For All Time" which feels really nice (like "small orbits big") but feels does not make "is" when you are doing science.

      Actually, most people seem to be arguing for the hydrostatic equilibrium definition, which is a consistent, clear-cut, and a very scientific definition of what is and is not a planet. And yes, we all know that means there are actually far more than 9 planets by that definition - I don't see anyone here arguing that that "planet" should include Pluto but not objects like Ceres.

      It's the people who have decided that there should only be eight planets in the solar system that are dancing around trying to create a definition that includes those eight objects and excludes all other objects. Of course, you can work backwards to create some arbitrary definition to do so for that works for the solar system, but you'll more than likely run into problems with other solar systems where things may not be so clear-cut. I mean, those objects orbiting other stars that Kepler keeps finding we have been calling planets, but that's a bit presumptuous because we can't actually know if they really are planets because we have no way to know if they have actually "cleared" their orbits - which just shows how poorly thought out the IAU definition is. But using hydrostatic equilibrium as the definition of a planet can be applied consistently everywhere, and with that definition there's no question those objects are planets. Of course, the IAU gets around that problem by defining a planet as something that only orbits our Sun, which is also ridiculous.